Universal Automaton enters the battlefield, triggering Sethron, creating a 2/2 Minotaur creature token.
The Minotaur enters the battlefield, triggering Cloudstone Curio, returning Universal Automaton from the battlefield to your hand.
Activate Ashnod's Altar by sacrificing the Minotaur token, adding CC.
Repeat.
This clever loop hinges on Universal Automaton's changeling nature, allowing it to count as a Minotaur the moment it hits the battlefield alongside Sethron, Hurloon General. That entrance triggers Sethron to forge a fresh Minotaur token, which in turn triggers Cloudstone Curio to bounce Universal Automaton right back to your hand for reuse. Meanwhile, Ashnod's Altar converts the freshly minted Minotaur token into a pair of colorless mana to fund the next iteration, leaving you with an unstoppable cycle of endless tokens, triggers, and mana.